JPH04293234A - Etching method of sic - Google Patents

Abstract

PURPOSE:To realize etching of SiC with high efficiency, by plasma-etching the SiC substrate surface by using mixed gas of gas having reactivity with silicon carbide (Sin) and inert gas. CONSTITUTION:Resist 11 is spread on the surface of an SiC substrate 10. After the resist 11 is fixed by baking the SiC substrate 10, ultraviolet rays are projected via a hard mask 13 patterned with Cr. A resist pattern 11b is formed on the SiC substrate 10 by eliminating the exposed part with exclusive developer, and vertical incidence etching is performed with an ion beam 15 using mixed gas of Ar and CHF3. The resist pattern 11b is subjected to ashing and eliminated, thereby completing the etching of SiC. Thus SiC can be etched with high efficiency.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly efficient etching method for SiC (silicon carbide) and a method for manufacturing SiC diffraction gratings, which is one of its applications.

0002

[Prior Art] Diffraction gratings for synchrotron radiation light (SOR light) and short-wavelength, high-power lasers are stable up to relatively high temperatures against temperature rises caused by these high-energy radiations, and have good thermal conductivity. SiC diffraction gratings are considered ideal because of their high cooling efficiency. However, even if you try to score the diffraction grating pattern directly on the SiC substrate by dry etching such as ion beam method, the resist will be etched faster than the SiC substrate, so the diffraction grating pattern will be formed directly on the SiC substrate. It was difficult to do so. Conventionally, diffraction gratings have been manufactured by coating a soft metal such as Au (gold) on a SiC substrate and mechanically carving grating grooves in the metal layer using a ruling engine, etc., as shown in Figure 5. Was.

0003

[Problems to be Solved by the Invention] Although the above-mentioned conventional diffraction grating uses SiC as a substrate, when the output of the SOR light or laser to be diffracted is very large, the SiC substrate and the metal may be damaged due to temperature rise. Distortion and peeling between the substrate and the metal layer occur due to the difference in thermal expansion coefficient between the two layers, resulting in problems such as a loss of accuracy and an unusable state. In order to avoid such inconveniences, if a diffraction grating is constructed using only a SiC substrate, it is necessary to directly score grating grooves on the SiC substrate. Pattern etching was also difficult. To explain this in detail, when dry etching a ceramic substrate, it is generally effective to perform RIE (reactive ion etching) using a gas that is reactive to the substrate material, but in the case of SiC Even if a gas reactive with SiC, such as CHF3, is used, the etching rate of the resist for forming a pattern is higher than the etching rate of SiC. For this reason,
In particular, in the case of a blazed type diffraction grating, it is difficult to make the cross-sectional shape of the grating groove into an ideal sawtooth shape.

[0004] As a method for directly etching a SiC substrate, a method has been proposed in which high-power SOR light is irradiated in a gas atmosphere (Proceedings of the 1990 Spring Conference of the Japan Society of Applied Physics, p. 500). However, this method can only be carried out at synchrotron facilities, which exist in only a few locations around the world, making it difficult to use it industrially. In view of the above, an object of the present invention is to provide a method that can directly etch a diffraction grating or the like on SiC using an industrially practicable method.

[0005]

[Means for Solving the Problems] The SiC etching method according to the present invention etches the surface of a SiC substrate by plasma etching using a gas that is a mixture of a gas that is reactive with SiC and an inert gas. The idea is to do so. Examples of gases reactive with SiC include CHF3, CF4, SF6, CCl4, and Cl2. Further, although Ar is a typical inert gas, the present invention is not limited thereto, and any single gas in group 0 of the periodic table, such as Ne or Kr, or a mixture thereof can be used. .

[0006]

In the plasma etching process, reactive gases are ionized, accelerated by an electric field, and impinge on the surface of a SiC substrate. In addition to the physical etching caused by the ion collision, etching of the SiC surface is promoted by a chemical reaction between the ions of the reactive gas and the SiC. In the case of conventional plasma etching using only reactive gas, C (carbon) generated by the reaction between reactive gas ions and SiC is deposited on the SiC substrate surface.
It acted to prevent further etching. For this reason, the above-mentioned phenomenon occurred in that the etching rate was higher in the resist portion than in the SiC substrate portion. In contrast, in plasma etching using a mixed gas with an inert gas according to the present invention, the ion beam generated by the inert gas plasma removes the C deposited layer, which is a reaction product, so the etching rate in the SiC substrate portion does not decrease. , the resist portion is etched at a speed equal to or faster than that of the resist portion.

[0007]

EXAMPLE First, the difference in etching rate between a SiC substrate and a resist was measured between a method according to the present invention and a conventional method. In both cases, etching was performed using an ion beam method, and the SiC substrate was etched by CVD (Chemical Vapor Depot) on a SiC substrate created by sintering.
SiC was further deposited using a photoresist, and as a resist, OFPR5000 (manufactured by Tokyo Ohka Co., Ltd.), which is a novolak-based positive resist, was used. First, etching was performed using only CF4 as a reactive gas and a single gas without mixing with an inert gas. In this case, the etching rate of SiC is 72.1 (angstroms/min)/(mA/cm2), while the etching rate of resist is 261.3 (angstroms/min)/(mA/cm2). SiC
Much larger than the substrate part, the Si against the resist
The selectivity ratio (etching rate ratio) of C is only 0.27.
It was 6. Next, CHF3 was used as a reactive gas, and etching was similarly performed using a single gas without mixing with an inert gas. In this case, the etching rate is 27
．． 6 (angstrom/min)/(mA/cm2)
, resist is 99.0 (angstroms/min)/
(mA/cm2), the etching rate of both of them was lower than that of CF4, but the selectivity of SiC was 0.279, which was almost the same as above. Finally, the etching rates were compared using only Ar gas, which is an inert gas. In this case, the etching rate of SiC is 94.6 (angstroms/min)/(mA/cm2), and the etching rate of resist is 325.0 (angstroms/min)/(mA/cm2).
min)/(mA/cm2), and the selectivity ratio of SiC was 0.291, indicating that the resist was much more easily etched, similar to the above two examples. On the other hand, when ion beam etching was performed using a mixed gas of Ar:CHF3=67:33,
The etching rate of SiC is 164.2 (angstroms/min)/(mA/cm2), and the etching rate of resist is 126.9 (angstroms/min)/(
mA/cm2), and the SiC selectivity was 1.29. That is, SiC is more easily etched than resist, indicating that pattern etching of SiC can be performed by the method according to the present invention.

Next, FIG. 1 shows the process of forming a specific pattern on the surface of SiC using the etching method according to the present invention.
This is explained by: First, a SiC substrate (CVD-Si
C) 10 is prepared, and as shown in FIG.
It is applied to a thickness of about 0.000 angstroms. After fixing the resist 11 by baking this substrate in a fresh air oven at 90°C for 30 minutes,
), ultraviolet rays 14 are irradiated through a hard mask 13 patterned with Cr (symbol 12 indicates a patterned layer in the figure). After that, the exposed area is removed using a special developer to form a resist pattern 11b on the SiC substrate 10 (FIG. 1(c)), and a mixed gas of Ar and CHF3 (mixing ratio Ar:CHF3=67:33) is formed on the SiC substrate 10. Direct-injection etching with the ion beam 15 is performed (FIG. 1(d)). Finally, the resist pattern 11b is ashed and removed using O2 plasma to complete the SiC etching (FIG. 1(e)).
. In the case of this example, the etching depth of the SiC substrate 10 under the above conditions was about 1000 angstroms.

Next, an example of manufacturing a SiC diffraction grating using the method according to the present invention will be described. FIG. 2 is an explanatory diagram of the process of manufacturing a laminar type diffraction grating. First, a SiC substrate 20 is prepared in which SiC is further deposited by CVD on SiC produced by sintering, and after optical polishing, a positive resist (for example, OFPR5000 mentioned above) 2 is applied to the surface.
Spin coat 1. Here, the film thickness of the resist 21 is, for example, about 3000 angstroms. Place this board in a fresh air oven at 90℃
Baking is performed for 30 minutes to fix the resist 21 (FIG. 2(a)). Next, the surface of the resist 21 is exposed to holographic exposure (
interference fringe exposure) is performed (FIG. 2(b)). The resist 21 exposed in this way is treated with a special developer (for example, NMD).
-3) to form a photoresist pattern 21b having a planar shape of equally spaced parallel lines and a sinusoidal cross-sectional shape. At this time, by setting the exposure time and development time to appropriate values, the resist 21 is completely removed at the trough of the sine wave, exposing the SiC substrate 20, and furthermore, the portion covered with the resist pattern 21b is removed. and the exposed portion of the SiC substrate 20 (L&S ratio) is set to a predetermined value. Next, using this photoresist pattern 21b as an etching mask, a mixed gas of Ar+CHF3 (mixture ratio is Ar:C) is etched from a direction perpendicular to the substrate 20.
Etching is performed using the ion beam 23 of HF3=67:33). As a result, as shown in FIG. 2(c),
The exposed portion of the SiC substrate 20 is selectively and strongly etched, and most of the resist 21b remains unetched because the etching speed is slow. When the etching depth of the SiC substrate 20 reaches a predetermined value, irradiation with the ion beam 23 is stopped, and the remaining resist 21b is removed by ashing with O2 plasma. As a result, the SiC substrate 20
A laminar diffraction grating with direct score lines is obtained (FIG. 2(d)). In addition, in the final remaining resist removal step, the SiC substrate 20 is not attacked by O2 plasma, and the cross-sectional shape formed by etching is maintained as it is.

FIG. 3 briefly shows the process of manufacturing a blazed type SiC diffraction grating. SiC substrate 30 having a photoresist pattern 31b manufactured in the process of FIG. 2(b)
Next, the same ion beam 34 as in the above embodiment is irradiated obliquely (FIG. 3(a)), and the cross section of the SiC substrate 30 is etched into a sawtooth shape. Here, by appropriately adjusting the thickness of the resist 31b in advance, the entire resist 31b is also removed by ion beam irradiation just when the etching depth of the SiC substrate 30 reaches a predetermined value. As a result, when the ion beam irradiation is completed, the time shown in Fig. 3 (
As shown in b), a blazed diffraction grating in which the SiC substrate 30 is directly scored is immediately obtained.

In the above embodiments, Ar is used as the inert gas and CHF3 is used as the reactive gas in the mixed gas, but it is of course possible to use the other inert gases and reactive gases mentioned above. . In addition, the mixing ratio of inert gas and reactive gas was 67:3 in each of the above examples.
3 (approximately 2:1), but this value was adopted as the most efficient value in the case of a mixed gas of Ar and CHF3, and is merely an example. According to experiments, Ar and C
In the case of a mixed gas of HF3, by increasing the amount of Ar (that is, making the Ar content 50% or more), the etching selectivity for the SiC resist can be increased compared to Ar alone or CHF.
3 can be made higher than when performing ion beam etching using a single gas. Of course, this range and the optimum mixing ratio depend on the type of gas to be mixed and the formation state of the SiC substrate (for example, sintered SiC substrate as is, sintered SiC+CV
D-SiC, SiC deposited by CVD on a sintered C substrate, etc.). Furthermore, it is clear from its principle that the etching method of the present invention is not limited to the ion beam etching used in the embodiments, but can be used for plasma etching in general.

0012

Effects of the Invention As described above, the SiC etching method according to the present invention allows the etching rate of SiC during plasma etching to be equal to or higher than the etching rate of the resist.
Pattern etching of the iC substrate becomes possible. Therefore, by directly scoring a diffraction grating pattern on a SiC substrate using the etching method according to the present invention, it is possible to manufacture a diffraction grating made only of SiC that has excellent heat resistance and good cooling efficiency. can.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a process of pattern etching a SiC substrate.

FIG. 2 is an explanatory diagram of the process of directly scoring a laminar diffraction grating on a CVD-SiC substrate.

FIG. 3 is an explanatory diagram of the process of directly scoring a blazed diffraction grating on a CVD-SiC substrate.

FIG. 4 is a cross-sectional view of a conventional diffraction grating in which an Au layer on a SiC substrate is scored with parallel lines.

[Explanation of symbols]

10, 20, 30, 40...SiC substrate 11, 21, 31...Resist layer 11b, 21b, 31b...Resist pattern 15, 23
, 34...Ion beam

Claims (2)

[Claims] 1. A method for etching SiC, which comprises etching the surface of a SiC substrate by plasma etching using a mixture of a gas reactive with SiC and an inert gas. 2. A resist layer having a diffraction grating pattern is formed on the surface of the SiC substrate, and then the resist layer is etched by plasma etching using a mixture of a gas reactive with SiC and an inert gas. A method for manufacturing a SiC diffraction grating, which comprises etching the surface of a SiC substrate.